ACPT-1599:

Updating unit tests so that we can verify that the config files don't get reloaded each time we get a key that doesn't exist in config.
Also adding test to confirm that we can reload config after reset to load previously unset config key.

Author: JacobBrownAustin

lib/internal/Magento/Framework/App/Test/Unit/DeploymentConfigTest.php

@@ -306,15 +306,11 @@ public function testEnvVariablesSubstitution(): void
      * @throws FileSystemException
      * @throws RuntimeException
      */
-    public function testReloadDataOnMissingConfig(): void
+    public function testShouldntReloadDataOnMissingConfig(): void
     {
-        $this->readerMock->expects($this->exactly(2))
+        $this->readerMock->expects($this->once())
             ->method('load')
-            ->willReturnOnConsecutiveCalls(
-                ['db' => ['connection' => ['default' => ['host' => 'localhost']]]],
-                [],
-                []
-            );
+            ->willReturn(['db' => ['connection' => ['default' => ['host' => 'localhost']]]]);
         $connectionConfig1 = $this->deploymentConfig->get(
             ConfigOptionsListConstants::CONFIG_PATH_DB_CONNECTIONS . '/' . 'default'
         );
@@ -330,4 +326,39 @@ public function testReloadDataOnMissingConfig(): void
         $result3 = $this->deploymentConfig->get('missing/key');
         $this->assertNull($result3);
     }
+
+    /**
+     * @return void
+     */
+    public function testShouldntLoadMultipleTimes() : void
+    {
+        $this->readerMock->expects($this->once())->method('load')
+            ->willReturn(['a' => ['a' => ['a' => 1]]]);
+        $this->deploymentConfig->get('a/a/a');
+        $this->deploymentConfig->get('a/a/b');
+        $this->deploymentConfig->get('a/a/c');
+        $this->deploymentConfig->get('a/b/a');
+        $this->deploymentConfig->get('a/b/b');
+        $this->deploymentConfig->get('a/b/c');
+    }
+
+    /**
+     * @return void
+     */
+    public function testShouldReloadPreviouslyUnsetKeysAfterReset() : void
+    {
+        $testValue = 42;
+        $loadReturn = ['a' => ['a' => ['a' => 1]]];
+        $this->readerMock->expects($this->any())->method('load')
+            ->will($this->returnCallback(function() use (&$loadReturn) { return $loadReturn;}));
+        $this->deploymentConfig->get('a/a/a');
+        $abcReturnValue1 = $this->deploymentConfig->get('a/b/c');
+        $this->assertNull($abcReturnValue1); // first try, it isn't set yet.
+        $loadReturn = ['a' => ['a' => ['a' => 1], 'b' => ['c' => $testValue]]];
+        $this->deploymentConfig->resetData();
+        $this->deploymentConfig->get('a/a/a');
+        $abcReturnValue2 = $this->deploymentConfig->get('a/b/c');
+        $this->assertEquals($testValue, $abcReturnValue2); // second try, it should load the newly set value
+    }
+
 }